The present proposal is an important step in discovering the neural mechanisms underlying spatial navigation, which requires continual updating of an individual's body position and movements relative to the location of a desired goal. The head direction (HD) signal, which includes spatial landmark and self- movement information, is thought to be the neural representation of an individual's direction. The network of brain structures involved in HD signal generation and control have been discovered in previous studies but the nature of information contributed by each brain structure remains unclear. The proposed experiments are designed to assess several key aspects of the HD signal, including: 1) the contribution of the postsubiculum (PoS) to the HD signal: 2) the type(s) of vestibular information included in the HD signal; and 3) the mechanism responsible for disruption of the HD signal during inverted locomotion. Specifically, HD activity will be assessed in rats following PoS lesion; HD activity will be assessed in mice lacking gravireceptors during upright and inverted locomotion. Results will provide a greater understanding of the HD signal's information content and may enable more effective treatments for disorders related to vestibular dysfunction. [unreadable] [unreadable] [unreadable]